Optical information recording medium

ABSTRACT

An optical information recording medium includes: a substrate; two or more information signal layers provided on the substrate; and a cover layer provided on the information signal layers. At least one of the two or more information signal layers is provided with an inorganic recording layer including Pd oxide, a first protective layer provided on a first main surface of the inorganic recording layer, and a second protective layer provided on a second main surface of the inorganic recording layer. And at least one of the first protective layer and the second protective layer includes a compound oxide of Si oxide, In oxide and Zr oxide as a main component.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 13/355,807 filed on Jan. 23, 2012, whichapplication claims priority to Japanese Priority Patent Application JP2011-022182 filed in the Japan Patent Office on Feb. 3, 2011, the entirecontent of which is hereby incorporated by reference.

BACKGROUND

The present disclosure relates to an optical information recordingmedium. More specifically, the present disclosure relates to an opticalinformation recording medium having two or more information signallayers.

Hitherto, CDs (Compact Discs) and DVDs (Digital Versatile Discs) and thelike have driven the market for optical information recording media.However, in recent years, there has been a demand for opticalinformation recording media with a further increased capacityaccompanying a rapid increase in data handled by high definitiontelevisions and PCs (Personal Computers). Mass storage opticalinformation recording media for blue lasers such as BD (Blu-ray Disc(registered trademark)) have been developed to meet such a demand andthe market for new, mass storage optical information recording media iscontinuing to grow.

As recordable optical information recording media, there are rewritableoptical information recording media as represented by CD-RW (CompactDisc-ReWritable), and DVD±RW (Digital Versatile Disc±ReWritable), aswell as write-once optical information recording media as represented byCD-R (Compact Disc-Recordable), and DVD-R (Digital VersatileDisc-Recordable). In particular, the latter have contributed greatly tothe expansion of the market as low cost media. Accordingly, with largecapacity optical information recording media for blue lasers as well, itis necessary to lower the price of write-once optical informationrecording media in order to expand the market. Furthermore, it isgenerally said that the storage reliability of the optical informationrecording media is high compared to hard disk drives (HDD), flash memoryand the like due to the recording and reproduction principles thereof,with the result that in recent years such media have been in more andmore demand as archival media such as those which are beginning to beused to store important information.

As the recording material used in write-once optical informationrecording media, there are inorganic material and organic coloringmaterial. In a typical write-once optical information recording medium,organic coloring materials have been primarily studied as the recordingmaterial. However, in the large-capacity optical information recordingmedia of recent years, inorganic materials have been studied extensivelyas the recording material.

For example, in Japanese Unexamined Patent Application Publication No.2010-218636, an optical information recording medium having an inorganicrecording layer including Pd and O is proposed. In addition, in asimilar optical information recording medium in Japanese UnexaminedPatent Application Publication No. 2009-129526, an optical informationrecording medium, which is provided with a protective layer of a mixture(ITO) of indium oxide and tin oxide as a main component on at least onesurface of the inorganic recording layer including Pd and O in order toachieve both storage reliability and good productivity, is proposed.

SUMMARY

However, there are difficulties in obtaining a favorable power marginwith the optical information recording medium provided with a protectivelayer of a mixture (ITO) of indium oxide and tin oxide as a maincomponent on at least one surface of the inorganic recording layer.

It is desirable to provide an optical information recording mediumhaving a favorable power margin.

According to a first embodiment of the present disclosure, there isprovided an optical information recording medium including: a substrate;two or more information signal layers provided on the substrate; and acover layer provided on the information signal layers, in which at leastone layer out of the two or more information signal layers is providedwith an inorganic recording layer including Pd oxide, a first protectivelayer provided on a first main surface of the inorganic recording layer,and a second protective layer provided on a second main surface of theinorganic recording layer, and in which at least one of the firstprotective layer and the second protective layer includes a compoundoxide of Si oxide, In oxide, and Zr oxide as a main component.

According to a second embodiment of the present disclosure, there isprovided an optical information recording medium recording layer thatincluding: a substrate; two or more information signal layers providedon the substrate; and a cover layer provided on the information signallayers, in which at least one layer out of the two or more informationsignal layers is provided with an inorganic recording layer including Pdoxide, a first protective layer provided on a first main surface of theinorganic recording layer, and a second protective layer provided on asecond main surface of the inorganic recording layer, and in which atleast one of the first protective layer and the second protective layerincludes a compound oxide of In oxide, Ga oxide, and Zn oxide as a maincomponent.

In the first and second embodiments, the thickness of the cover layer isnot particularly limited, and the cover layer includes the substrate, asheet, the coating layer and the like. As a preferable high-densityoptical information recording medium, there is one having aconfiguration in which, with the use of a high NA objective lens, a thinlight transmissive layer such as a sheet or a coating layer is adoptedas a cover layer, and the recording and reproduction of informationsignals is performed by irradiating light from the side of the lighttransmissive layer. In such a case, it is possible to adopt an opaquesubstrate as the substrate. The light incidence plane for recording andreproducing the information signal is appropriately set to at least onesurface of the cover layer side and the substrate side according to theformat of the optical information recording medium.

In the first and second embodiments, the inorganic recording layerpreferably includes W oxide, Pd oxide and Cu oxide as a main componentand even more preferably includes Zn oxide in addition to these oxides.

In the first and second embodiments, one surface of either the substrateside or the cover layer side is preferably a light irradiation plane onwhich light for recording or reproducing an information signal on two ormore information signal layers is irradiated.

In the first embodiment, it is preferable that the layer out of thefirst protective layer and the second protective layer, which is on theopposite side to the light irradiation plane, include a compound oxideof Si oxide, In oxide, and Zr oxide, and it is preferable that both ofthe first protective layer and the second protective layer include acompound oxide of Si oxide, In oxide and Zr oxide as a main component.

In the first embodiment, it is preferable that at least one layer out ofthe information signal layers other than the information signal layerfurthest to the back from the light irradiation plane is an informationsignal layer in which at least one of the first protective layer and thesecond protective layer includes a compound oxide of Si oxide, In oxideand Zr oxide as a main component. It is preferable that the inorganicrecording layer of the information signal layer which is closest to thelight irradiation plane out of the two or more information signal layersis an information signal layer in which at least one of the firstprotective layer and the second protective layer includes a compoundoxide of Si oxide, In oxide and Zr oxide as a main component.

In the second embodiment, it is preferable that the layer out of thefirst protective layer and the second protective layer which is theopposite side to the light irradiation plane include a compound oxide ofIn oxide, Ga oxide and Zn oxide and it is preferable that both the firstprotective layer and the second protective layer include a compoundoxide of In oxide, Ga oxide, and Zn oxide as a main component.

In the first embodiment, it is preferable that at least one layer out ofthe information signal layers other than the information signal layerfurthest to the back from the light irradiation plane be an informationsignal layer in which at least one of the first protective layer and thesecond protective layer includes a compound oxide of In oxide, Ga oxideand Zn oxide as a main component. It is preferable that the inorganicrecording layer of the information signal layer which is closest to thelight irradiation plane out of the two or more information signal layersbe an information signal layer in which at least one of the firstprotective layer and the second protective layer includes a compoundoxide of In oxide, Ga oxide and Zn oxide as a main component.

As described above, according to the embodiments, it is possible torealize an optical information recording medium having a favorable powermargin.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a schematic cross-sectional view showing an exampleconfiguration of an optical information recording medium according toone embodiment of the present disclosure and FIG. 1B is a schematicdiagram showing a configuration example of each information signal layershown in FIG. 1A.

FIG. 2A is a graph showing the power margin of the optical informationrecording medium in Test Example 1-1 and FIG. 2B is a graph showing thepower margin of the optical information recording medium in Test Example1-2.

FIG. 3 is a graph showing the power margin of the optical informationrecording medium in Test Example 1-3.

FIG. 4A is a graph showing the power margin of the optical informationrecording medium in Test Example 1-4 and FIG. 4B is a graph showing thepower margin of the optical information recording medium in Test Example1-5.

FIG. 5 is a graph showing the power margin of the optical informationrecording medium in Test Example 2.

FIG. 6 is a graph showing the power margin of the optical informationrecording media in Test Examples 3-3 to 3-4.

FIG. 7A is a graph showing the relationship between the variable x andthe transmittance in the optical information recording media of TestExamples 4-1 to 4-13 and FIG. 7B is a graph showing the relationshipbetween the transmittance and the optimal recording power Pwo in theoptical information recording media of Test Examples 4-1 to 4-13.

FIG. 8 is a graph showing the composition ratio of the inorganicrecording layer in the optical information recording media of TestExamples 4-1 to 4-13.

FIG. 9A is a graph showing the relationship between the i-MLSE of the L0layer and the reflectance of the L0 layer in the optical informationrecording media of Test Examples 5-1 to 5-12, FIG. 9B is a graph showingthe relationship between the reflectance of the L layer and thereflectance of the L0 layer in the optical information recording mediaof Test Examples 5-13 to 5-24, and FIG. 9C is a graph showing therelationship between the transmittance of the L layer and the i-MLSE ofthe L0 layer in the optical information recording media of Test Examples6-1 to 6-9.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described below withreference to the drawings.

[Configuration of the Optical Information Recording Medium]

FIG. 1A is a schematic cross-sectional view showing an exampleconfiguration of an optical information recording medium according toone embodiment of the present disclosure. The optical informationrecording medium 10 is a so-called write-once optical informationrecording medium, and, as shown in FIG. 1A, has a configuration in whichan information signal layer L0, an intermediate layer S1, an informationsignal layer L1, an intermediate layer S2, an information signal layerL2, an intermediate layer S3, an information signal layer L3, and alight transmissive layer 2 which is a cover layer are laminated in suchan order on the main surface of the substrate 1. If necessary, a hardcoat layer 3 may further be provided on the surface of the lighttransmissive layer 2. If necessary, a barrier layer 4 may further beprovided on the surface of the substrate 1 side. In the descriptionbelow, information signal layer L is used where no particulardistinction is made between the information signal layers L0 to L3.

In the optical information recording medium 10 according to the firstembodiment, recording and reproduction of the information signal isperformed by irradiating the laser beam from the surface C of the lighttransmissive layer 2 side to each of the information signal layers L0 toL3. For example, recording and reproduction of the information signal isperformed by condensing a laser beam having a wavelength range of 400 nmto 410 nm with an objective lens having a numerical aperture range of0.84 to 0.86, and irradiating the laser beam from the side of the lighttransmissive layer 2 to each of the information signal layers L0 to L3.As such an optical information recording medium 10, for example, BD-Rmay be exemplified. Below, the surface C which is irradiated by thelaser beam for recording or reproducing the information signal on theinformation signal layers L0 to L3 is called the light irradiation planeC.

Below, the substrate 1, the information signal layers L0 to L3,intermediate layers S1 to S3, light transmissive layer 2, hard coatlayer 3, and barrier layer 4 configuring the optical informationrecording medium 10 will be described in order.

(Substrate)

The substrate 1, for example, has a circular shape in which an openingis formed in the center (hereinafter, called the center hole). The mainsurface of the substrate 1, for example, is concavo-convex, and theinformation signal layer L0 is deposited on such a concavo-convexsurface. Below, in the concavo-convex surface, concave portions arereferred to as in-grooves Gin and convex portions are referred to ason-grooves Gon.

As the shape of the in-groove Gin and the on-groove Gon, for example,various shapes may be exemplified such as spiral shapes and concentriccircles. Further, the in-grooves Gin and/or the on-grooves Gon, forexample, are made to wobble (meander) in order to add linear velocitystability and address information.

The diameter of the substrate 1 may be selected as 120 mm for example.The thickness of the substrate 1 is selected while taking the stiffnessinto account and is preferably 0.3 mm to 1.3 mm, more preferably 0.6 mmto 1.3 mm; for example, 1.1 mm may be selected. Further, the diameter ofthe center hole may be selected as 15 mm, for example.

As the material of the substrate 1, for example, a plastic material orglass may be used, and, from a cost standpoint, it is preferable to usea plastic material. As the plastic material, for example, polycarbonateresins, polyolefin resins, acrylic resins, or the like may be used.

(Information Signal Layer)

FIG. 1B is a schematic diagram showing a configuration example of eachinformation signal layer shown in FIG. 1A. As shown in FIG. 1B, theinformation signal layers L0 to L3 are provided with an inorganicrecording layer 11 having an upper side surface (second main surface)and a lower side surface (first main surface), a first protective layer12 provided adjacently to the lower side surface of the inorganicrecording layer 11, and a second protective layer 13 provided adjacentlyto the upper side surface of the inorganic recording layer 11. Throughsuch a configuration, it is possible to improve the durability of theinorganic recording layer 11. Here, out of the two main surfaces of theinorganic recording layer 11, the upper side surface refers to the mainsurface irradiated with a laser beam for recording or reproducing aninformation signal and the lower side surface refers to the main surfaceopposite to the side irradiated with the above-described laser beam,that is, the main surface of the substrate side.

The main component of the inorganic recording layer 11 is preferably aninorganic recording material including Pd oxide (hereinafter referred toas “PdO-based material”). As PdO-based materials, for example, it ispossible to use a material having a main component having atwo-elemental compound oxide of In oxide and Pd oxide; however, the useof a three-elemental compound oxide of W oxide, Pd oxide and Cu oxide(hereinafter referred to as “WCPO”) is preferable and the use of afour-elemental compound oxide in which Zn oxide is further added to theWCPO (hereinafter referred to as “WZCPO”) is more preferable. By usingWCPO as the PdO-based materials, it is possible to achieve excellenttransmission characteristics while satisfying the characteristics askedfor the recording layer of the optical information recording medium. Byusing WZCPO as the PdO-based materials, it is possible to achieveexcellent transmission characteristics while satisfying thecharacteristics asked for the recording layer of the optical informationrecording medium and it is possible to reduce the content of W oxide, Pdoxide, and Cu oxide. By reducing the content of W oxide, Pd oxide, andCu oxide, in particular, Pd oxide, it is possible to reduce the cost ofthe optical information recording medium 10.

It is preferable that at least one layer of the inorganic recordinglayer 11 among the information signal layers L1 to L3 other than theinformation signal layer L0 furthest to the back from the lightirradiation plane C include WCPO as a main component. The ratio of W,Pd, and Cu included in the WCPO preferably satisfies the relationship0.17≦x₁, more preferably 0.37≦x₁, still more preferably 0.37≦x₁≦1.26,and most preferably 0.56≦x₁≦1.26. In such a manner, it is possible toachieve excellent transmission characteristics while satisfying thecharacteristics asked for the information signal layer of the opticalinformation recording medium. Here, the characteristics asked for theinformation signal layer of the optical information recording mediumare, for example, low i-MLSE, wide power margin, high reproductiondurability, suppression of changes in transmittance after recording, andthe like.

Here, x₁ is a variable defined as x₁=a/(b+0.8c).

a: atomic ratio (atomic %) of W with respect to the total of W, Pd, andCu

b: atomic ratio (atomic %) of Pd with respect to the total of W, Pd, andCu

c: atomic ratio (atomic %) of Cu with respect to the total of W, Pd, andCu

From the viewpoint of increasing the amount of light that reaches theinformation signal layer L0 furthest to the back from the lightirradiation plane C, it is preferable that all of the inorganicrecording layers 11 of the information signal layers L1 to L3 other thanthe information signal layer L0 have a high transmittance.

Further, in addition to the high transmittance, from the viewpoint ofsecuring the characteristics asked for the high transmittance layer evenat high transmittance, it is preferable that all of the inorganicrecording layers 11 of the information signal layers L0 to L3 includeWCPO as a main component. In such a case, the ratio of the W, the Pd,and the Cu that are included in the WCPO preferably satisfies therelationship 0.17≦x₁, more preferably satisfies the relationship0.37≦x₁, still more preferably satisfies the relationship 0.37≦x₁≦1.26,and most preferably satisfies the relationship 0.56≦x₁≦1.26. Further,the value of the variable x₁ of the inorganic recording layer 11 of theinformation signal layers L0 to L3 is preferably a value as great asthat of the information signal layer L close to the light irradiationplane C. The reason is that it is preferable to set the transmittance tobe as high as the information signal layer L close to the lightirradiation plane C.

The atomic ratio a of W with respect to the total of W, Pd, and Cu ispreferably within a range between 10 atomic % and 70 atomic %, and morepreferably within a range between 14.2 atomic % and 31.8 atomic %. Ifthe atomic ratio a is less than 10 atomic %, the transmittance tends tobe low. On the other hand, if the atomic ratio a exceeds 70 atomic %,the transmittance is high but the recording sensitivity tends to beinsufficient.

The atomic ratio b of Pd with respect to the total of the W, the Pd, andthe Cu is preferably within a range between 2 atomic % and 50 atomic %,and more preferably within a range between 4.4 atomic % and 32.2 atomic%. If the atomic ratio b is less than 2 atomic %, the recording powermargin tends to become narrow. On the other hand, if the atomic ratio bexceeds 50 atomic %, the transmittance tends to be low.

The atomic ratio c of Cu with respect to the total of the W, the Pd, andthe Cu is preferably within a range between 10% atomic % and 70% atomic%, and more preferably within a range between 28.5 atomic % and 68.1atomic %. If the atomic ratio c is less than 10 atomic %, thereproduction durability tends to decrease. On the other hand, if theatomic ratio c exceeds 70 atomic %, the transmittance tends to be low.

It is preferable that the inorganic recording layer 11 of at least onelayer out of the information signal layers L1 to L3 other than theinformation signal layer L0 that is furthest to the back of the lightirradiation plane C include WZCPO, in which Zn oxide is added to WCPO,as a main component. The ratio of the W, the Pd, the Cu, and the Zn thatare included in the WZCPO preferably satisfies the relationship 0.17≦x₂,more preferably satisfies the relationship 0.37≦x₂, still morepreferably satisfies the relationship 0.37≦x₂≦1.26, and most preferablysatisfies the relationship 0.56≦x₂≦1.26. In such a manner, it ispossible to achieve excellent transmission characteristics whilesatisfying the characteristics asked for the recording layer of theoptical information recording medium and it is possible to reduce thecontent of W oxide, Pd oxide, and Cu oxide. By reducing the content of Woxide, Pd oxide, and Cu oxide, in particular, Pd oxide included inprecious metals, it is possible to reduce the cost of the opticalinformation recording medium 10,

where x₂ is a variable defined by x₂=(0.1d+a)/(b+0.8c).

a: atomic ratio (atomic %) of W with respect to the total of W, Pd, Cu,and Zn

b: atomic ratio (atomic %) of Pd with respect to the total of W, Pd, Cu,and Zn

c: atomic ratio (atomic %) of Cu with respect to the total of W, Pd, Cu,and Zn

d: atomic ratio (atomic %) of Zn with respect to the total of W, Pd, Cu,and Zn

From the viewpoint of increasing the amount of light that reaches theinformation signal layer L0 furthest to the back from the lightirradiation plane C, it is preferable that all of the inorganicrecording layers 11 of the information signal layers L1 to L3 other thanthe information signal layer L0 have a high transmittance.

Further, in addition to the high transmittance, from the viewpoints ofsecuring the characteristics asked for the high transmittance layer evenat high transmittance and reducing the cost of the optical informationrecording medium, it is preferable that all of the inorganic recordinglayers 11 of the information signal layers L0 to L3 include WZCPO as amain component. In such a case, the ratio of the W, the Pd, and the Cuthat are included in the WZCPO preferably satisfies the relationship0.17≦x₂, more preferably satisfies the relationship 0.37≦x₂, still morepreferably satisfies the relationship 0.37≦x₂≦1.26, and most preferablysatisfies the relationship 0.56≦x₂≦1.26. In addition, the value of thevariable x₂ of the inorganic recording layer 11 of the informationsignal layers L0 to L4 is preferably a value as great as that of theinformation signal layer L close to the light irradiation plane C. Thereason is that it is possible to increase the transmittance to be ashigh as the information signal layer L close to the light irradiationplane C.

The atomic ratio a of W with respect to the total of W, Pd, Cu, and Znis preferably within a range between 10 atomic % and 70 atomic %, andmore preferably within a range between 14.2 atomic % and 31.8 atomic %.If the atomic ratio a is less than 10 atomic %, the transmittance tendsto be low. On the other hand, if the atomic ratio a exceeds 70 atomic %,the recording sensitivity tends to be insufficient.

The atomic ratio b of Pd with respect to the total of the W, the Pd, theCu, and the Zn is preferably within a range between 2 atomic % and 50atomic %, and more preferably within a range between 4.4 atomic % and32.2 atomic %. If the atomic ratio b is less than 2 atomic %, therecording power margin tends to become narrow. On the other hand, if theatomic ratio b exceeds 50 atomic %, the transmittance tends to be low.

The atomic ratio c of Cu with respect to the total of the W, the Pd, theCu, and the Zn is preferably within a range between 10% and 70%, andmore preferably within a range between 28.5 atomic % and 43.4 atomic %.If the atomic ratio c is less than 10 atomic %, the reproductiondurability tends to weaken. On the other hand, if the atomic ratio cexceeds 70 atomic %, the transmittance tends to be low.

The atomic ratio d of Zn with respect to the total of the W, the Pd, theCu, and the Zn is preferably within a range between 5% and 60%, and morepreferably within a range between 17 atomic % and 41 atomic %. If theatomic ratio d is less than 5 atomic %, the cost reducing effect tendsto weaken. On the other hand, if the atomic ratio d exceeds 60 atomic %,there is a tendency for storage reliability to deteriorate.

As the material of the information signal layers L1 to L3 other thanWCPO or WZCPO, for example, it is also possible to use a material inwhich the main component is a mixed oxide of In oxide and Pd oxide.However, from the viewpoint of achieving excellent transmissioncharacteristics while satisfying the characteristics asked for theinformation signal layer of the optical information recording medium, itis preferable to use WCPO or WZCPO.

As the material of the information signal layer L0 furthest to the backfrom the light irradiation plane C, for example, it is also possible touse a material in which the main component is a mixed oxide of In oxideand Pd oxide. However, from the viewpoint of a wide recording powermargin, it is preferable to use the above-described WCPO or WZCPO.

The thickness of the inorganic recording layer 11 is preferably within arange of 25 nm to 60 nm, and more preferably 30 nm to 50 nm. If thethickness is less than 25 nm, there is a tendency for the i-MLSE todeteriorate, the modulation rate to be low and the signal properties todeteriorate. On the other hand, if the thickness exceeds 60 nm, therecording power margin tends to become narrow.

It is preferable to use dielectric layers or transparent conductivelayers as the first protective layer 12 and the second protective layer13, and it is possible to use a dielectric layer for one of the firstprotective layer 12 and the second protective layer 13 and a transparentconductive layer for the other. Because the dielectric layers or thetransparent conductive layers function as oxygen barrier layers, it ispossible to improve the durability of the inorganic recording layers 11.Further, by suppressing oxygen from escaping from the inorganicrecording layers 11, it is possible to suppress changes (particularlyobservable as a decrease in the reflectance) in the film quality of therecording film, and it is possible to secure the necessarycharacteristics of the inorganic recording layers 11. Furthermore, byproviding dielectric layers or transparent conductive layers, it ispossible to improve the recording properties. It is considered that thereason is that because the thermal diffusion from laser beam that isincident on the dielectric layers or the transparent conductive layersis optimally controlled, bubbles on the recording portions may besuppressed from becoming too large and from popping due to thedisintegration of the Pd oxide progressing excessively, whereby it ispossible to optimize the shapes of the bubbles during recording.

It is preferable that at least one of the first protective layer 12 andthe second protective layer 13 include as a main component thethree-elemental compound oxides of Si oxide, In oxide, and Zr oxide(SiO₂—In₂O₃—ZrO₂ is below referred to as “SIZ”) as a compound oxide, orthe three elemental oxides of In oxide, Ga oxide, and Zn oxide(In₂O₃—Ga₂O₃—ZnO is below referred to as “IGZO”). In such a manner, itis possible to obtain a favorable power margin. Here, as the materialsof the first protective layer 12 and the second protective layer 13, itis possible to adopt the same material or composition ratio; however,without being limited to this example, different materials orcomposition ratios may be adopted as the materials of the firstprotective layer 12 and the second protective layer 13. For example,both the first protective layer 12 and the second protective layer 13may include SIZ or IGZO as a main component; however, without beinglimited to this example, one of the first protective layer 12 and thesecond protective layer 13 may include SIZ as a main component and theother may include IGZO as a main component.

In a case where at least one layer of the first protective layer 12 andthe second protective layer 13 includes SIZ or IGZO as a main component,it is preferable that, as the inorganic recording layer 11, a layerincluding WCPO as a main component be adopted and more preferable that alayer including WZCPO, in which Zn oxide is added to WCPO, as a maincomponent be adopted. In a case where the inorganic recording layer 11has WCPO or WZCPO as a main component, a more favorable power margin maybe obtained compared to a case where the inorganic recording layer 11has a PdO-based material other than WCPO or WZCPO as a main component.In a case where the inorganic recording layer 11 has WZCPO as a maincomponent, it is possible to further obtain the advantage that theoptical information recording medium 10 is reduced in cost. The reasonfor this is that, by making the WCPO further include Zn oxide, it ispossible to thin the entirety of the WZCPO with the Zn oxide, and, as aresult, decrease the content of Pd, which is a precious metal material.

For at least one layer out of the information signal layers L1 to L3other than the information signal layer L0 that is furthest to the backof the light irradiation plane C, it is preferable that at least onelayer of the first protective layer 12 and the second protective layer13 adopt a configuration that has SIZ or IGZO as a main component andmore preferable that both layers of the first protective layer 12 andthe second protective layer 13 adopt a configuration that has SIZ orIGZO as a main component. By adopting such a configuration, the hightransmittance may be maintained and it is possible to increase the lightquantity of laser beam that reaches the information signal layer L0.

From the viewpoint of maintaining a high light quantity of laser beamthat reaches the information signal layer L0, for all the informationsignal layers L1 to L3 other than the information signal layer L0 thatis furthest to the back of the light irradiation plane C, it ispreferable that at least one layer of the first protective layer 12 andthe second protective layer 13 adopt a configuration that has SIZ orIGZO as a main component and more preferable that both layers of thefirst protective layer 12 and the second protective layer 13 adopt aconfiguration that has SIZ or IGZO as a main component.

From the viewpoint of maintaining a high transmittance of theinformation signal layer L3 closest to the light irradiation plane C, atleast one layer of the first protective layer 12 and the secondprotective layer 13 of the information signal layer L3 preferably hasSIZ or IGZO with a low extinction coefficient as a main component and,more preferably, both layers have SIZ or IGZO as a main component. Thereason for maintaining the transmittance of the information signal layerL3 closest to the light irradiation plane C in the information signallayers L1 to L3 as high as possible is that, generally, in the balancingof the transmittance and the recording sensitivity which is inverselyproportional thereto, when a single layer of the information signallayer L3 is set with a high transmittance and a low recordingsensitivity, for a multi-layer layered medium, which is configured by acombination such that the transmittance is set as low as that of theinformation signal layer far from the light irradiation plane C of oneside and the sensitivity of a single layer is high, it is possible toapproximately fix the recording sensitivity of each layer set as amulti-layer medium by combining transmittance and sensitivity.

By setting SIZ or IGZO as the main component of one of the firstprotective layer 12 and the second protective layer 13, it is possibleto obtain a favorable power margin; however, from the viewpoint ofobtaining an even more favorable power margin, it is preferable thatboth the first protective layer 12 and the second protective layer 13include SIZ or IGZO as the main component. When adopting a configurationin which SIZ or IGZO is set as the main component of one of the firstprotective layer 12 and the second protective layer 13, it is preferablethat the first protective layer 12 provided on the lower side surface ofthe inorganic recording layer 11 have SIZ or IGZO as the main component.By including SIZ or IGZO as the main component in the first protectivelayer 12 provided on the lower side surface of the inorganic recordinglayer 11, it is possible to further increase the power margin incomparison to a case in which SIZ or IGZO is included as the maincomponent in the first protective layer 12 provided on the upper sidesurface of the inorganic recording layer 11.

In the case of a configuration including SIZ or IGZO as the maincomponent of one of the first protective layer 12 and the secondprotective layer 13, as the material to be set as the main component ofthe other layer, for example, it is possible to use a dielectricmaterial or a transparent conductive material, specifically, oxides,nitrides, sulfides, carbides, fluorides, or mixtures thereof may beused. As oxides, for example, one or more oxides of chemical elementsselected from the group consisting of In, Zn, Sn, Al, Si, Ge, Ti, Ga,Ta, Nb, Hf, Zr, Cr, Bi, and Mg may be exemplified. As the nitrides, forexample, one or more nitrides of chemical elements selected from thegroup consisting of In, Sn, Ge, Cr, Si, Al, Nb, Mo, Ti, Nb, Mo, Ti, W,Ta, and Zn, preferably, one or more nitrides of chemical elementsselected from the group consisting of Si, Ge and Ti, may be exemplified.As the sulfides, for example, Zn sulfide may be exemplified. As thecarbides, for example, one or more carbides of chemical elementsselected from the group consisting of In, Sn, Ge, Cr, Si, Al, Ti, Zr,Ta, and W, preferably, one or more carbides of chemical elementsselected from the group consisting of Si, Ti and W, may be exemplified.As the fluorides, for example, one or more fluorides of chemicalelements selected from the group consisting of Si, Al, Mg, Ca and La maybe exemplified. As mixtures of these, for example, ZnS—SiO₂,SiO₂—Cr₂O₃—ZrO₂ (SCZ), In₂O₃—SnO₂ (ITO), In₂O₃—CeO₂ (ICO), In₂O₃—Ga₂O₃(ITO), Sn₂O₃—Ta₂O₅ (TTO), TiO₂—SiO₂, and the like may be exemplified.

Specifically, it is preferable that SIZ or IGZO be included as the maincomponent of one of the first protective layer 12 and the secondprotective layer 13 and that ITO be included in the other and it is morepreferable that the first protective layer 12 include ITO as a maincomponent and the second protective layer 13 include SIZ or IGZO as amain component. In this manner, a certain amount of the high powermargin is sacrificed; however, this is because it is also possible tominimize changes in transmittance after recording. In the case of amulti-layer recording medium, layers other than the innermost layer areinformation signal layers for transmission and the balance between hightransmittance and transmittance variance after recording may be achievedaccording to the desired characteristics of each layer.

From the viewpoint of the sputtering rate, the In oxide content in SIZmay be 20 mol % or more, and from the viewpoint of storage reliability,is preferably 70 mol % or less. Further, in order that the SI oxide andthe Zr oxide function as a compound oxide, amounts of 15 mol % or moreand 50 mol % or less are preferable.

The thickness of the first protective layer 12 is preferably within arange of 2 nm to 20 nm. If the thickness is less than 2 nm, there is atendency for the barrier effect to the recording layer to be reduced. Onthe other hand, if the thickness exceeds 20 nm, there is a tendency forthe recording power margin to be reduced.

The thickness of the second protective layer 13 is preferably within arange of 2 nm to 50 nm. If the thickness is less than 2 nm, there is atendency for the barrier effect to the recording layer to be reduced. Onthe other hand, if the thickness exceeds 50 nm, there is a tendency forthe recording power margin to be reduced.

As information signal layers L0 to L3, it is preferable that ones havingthe configurations below be used in combination. The L1 layer, which isclose to the innermost layer having small x₁ and x₂ in composition ratioand asked to have a high sensitivity, is likely to have largetransmittance fluctuations after recording as the amounts of Pd and Cuare likely to be large. As a result, it is preferable to use a firstprotective layer 12 and a second protective layer 13 with an extinctioncoefficient of 0.05 or more and suppress transmittance fluctuations.Further, in the L3 layer which has large x₁ and x₂ in composition ratioand has to have a high transmittance, the transmittance fluctuationsafter recording are small but the power margin is likely to becomenarrow. As a result, it is preferable to use SIZ and IGZO in the firstprotective layer 12 and the second protective layer 13 and secure thepower margin. Further, when the L2 layer uses a combination of the L1layer and the L3 layer, it is possible to make the power margin andtransmittance fluctuation suppression characteristics of each layeruniform even when the material of the recording layer, the desiredsensitivity and the transmittance are different.

(Information Signal Layer L0)

First protective layer 12: ITO

Inorganic recording layer 11: WCPO (0.4≦x₁≦0.6), preferably WZCPO(0.4≦x₂≦0.6)

Second protective layer 13: ITO

(Information Signal Layer L1)

First protective layer 12: material with an extinction coefficient k ina range of 0.05 to 0.6, preferably ITO

Inorganic recording layer 11: WCPO (0.5≦x₁≦0.9), preferably WZCPO(0.5≦x₂≦0.9)

Second protective layer 13: material with an extinction coefficient k ina range of 0.05 to 0.6, preferably ITO

(Information Signal Layer L2)

First protective layer 12: material with an extinction coefficient k ina range of 0.05 to 0.6, preferably ITO

Inorganic recording layer 11: WCPO (0.8≦x₁≦1.2), preferably WZCPO(0.8≦x₂≦1.2)

Second protective layer 13: SIZ or IGZO

(Information Signal Layer L3)

First protective layer 12: SIZ or IGZO

Inorganic recording layer 11: WCPO (0.8≦x₁≦1.2), preferably WZCPO(0.8≦x₂≦1.2)

Second protective layer 13: SIZ or IGZO

(Intermediate Layer)

The intermediate layers S1 to S3 fulfill a role of separating the L0,L1, L2, and L3 so as to have a sufficient physical and optical distance,are provided with a concavo-convex surface on the surfaces thereof, andform concentric circle or spiral shaped grooves (in-groove Gin andon-groove Gon). The thickness of the intermediate layers S1 to S3 ispreferably set to 9 μm to 50 μm, for example, S1=15 μm, S2=20 μm, andS3=10 μm. The material of the intermediate layers S1 to S3 is notparticularly limited, but it is preferable to use an ultraviolet curableacrylic resin, in addition, it is preferable that the intermediatelayers S1 to S3 have a sufficiently high light transmittance since theywill be optical paths for laser beam for the purpose of recording andreproducing data to and from the inner layers.

(Light Transmissive Layer)

The light transmissive layer 2, for example, is a resin layer formed bycuring a photosensitive resin such as an ultraviolet curable resin. Asthe material of such a resin layer, for example, ultraviolet curableacrylic resins may be exemplified. Further, the light transmissive layer2 may be configured of a light transmitting sheet having a circularshape and an adhesive layer for making the light transmitting sheetadhere to the substrate 1. It is preferable that the light transmittingsheet be material with low absorbance with respect to the laser beamused in recording and reproduction, specifically, a material with atransmittance of 90% or more is preferable. As the material of thelight-transmitting sheet, for example, a polycarbonate resin material, apolyolefin resin (for example, ZEONEX (registered trademark)), and thelike may be used. As the material of the adhesive layer, for example, anultraviolet curable resin, a pressure sensitive adhesive (PSA: PressureSensitive Adhesive), or the like, may be used.

The thickness of the light transmissive layer 2 is preferably selectedfrom a range of 10 μm to 177 μm, for example, set as 53.5 μm. Bycombining such a thin light transmissive layer 2 and, for example, anobjective lens made to have a high NA (numerical aperture) ofapproximately 0.85, it is possible to realize high density recording.

(Hard Coat Layer)

The hard coat layer 3 is for conferring anti-scratching properties andthe like on the light irradiation plane C. As the material of the hardcoat layer 3, for example, an acrylic resin, a silicone resin, afluorine resin, an organic inorganic hybrid resin, or the like may beused.

(Barrier Layer)

The barrier layer 4 is for suppressing outgassing (moisture release)from the back face of the substrate 1 during the film forming process.Further, the barrier 4 also functions as a moisture-proof layer thatsuppresses the absorption of moisture on the back face of thesubstrate 1. Although the material that configures the barrier layer 4is not particularly limited as long as the outgassing (moisture release)from the back face of the substrate 1 is able to be suppressed, to givean example, a dielectric with low gas transmission may be used. As sucha dielectric, for example, SiN, SiO₂, TiN, AlN, ZnS—SiO₂, or the likemay be used. The thickness of the barrier layer 4 is preferably set tobetween 5 nm and 40 nm. If the thickness is less than 5 nm, the barrierfunction of suppressing outgassing from the substrate back face tends todecrease. This is because, on the other hand, if the thickness isgreater than 40 nm, there is hardly any difference in the barrierfunction of suppressing outgassing compared to a case when the thicknessis lower, and further, productivity tends to decrease. It is preferablethat the moisture transmittance of the barrier 4 be equal to or lessthan 5×10⁻⁵ g/cm² per day.

In the optical information recording medium 10 having the aboveconfiguration, when the laser beam is irradiated to the inorganicrecording layer 11, Pd oxide is heated and decomposed by the laser beamto release oxygen and bubbles are generated in the parts irradiated withlaser beam. In this manner it is possible to irreversibly record theinformation signal.

[Manufacturing Method of Optical Information Recording Medium]

Next, an example of a manufacturing method of an optical informationrecording medium according to an embodiment of the present disclosurewill be described.

(Formation Process of Substrate)

First, the substrate 1 in which a concavo-convex surface is formed onthe principal surface is formed. As the formation method of thesubstrate 1, for example, an injection method, a photopolymerizationmethod (2P method), and the like may be used.

(Formation Process of Information Signal Layers)

Next, the information signal layer L0 is formed by sequentiallylaminating the first protective layer 12, the inorganic recording layer11, and the second protective layer 13 on the substrate 1 by asputtering method, for example. The formation process of the firstprotective layer 12, the inorganic recording layer 11, and the secondprotective layer 13 will be described below in detail.

(Film Forming Process of First Protective Layer)

First, the substrate 1 is transported into a vacuum chamber in which atarget for the first protective layer formation, and the inside of thevacuum chamber is vacuumed until the vacuum chamber reaches apredetermined pressure. The first protective layer 12 is then formed onthe substrate 1 by sputtering the target while introducing a process gassuch as Ar gas or O₂ gas into the vacuum chamber. Although a radiofrequency (RF) sputtering method or a direct current (DC) sputteringmethod, for example, may be used as the sputtering method, the directcurrent sputtering method is particularly preferable. The reason is thatsince the direct current sputtering method has a high film forming ratecompared to the radio frequency sputtering method, it is possible toimprove productivity.

(Film Forming Process of Inorganic Recording Layer)

Next, the substrate 1 is transported into a vacuum chamber in which atarget for inorganic recording layer film formation use is provided, andthe inside of the vacuum chamber is vacuumed until the vacuum chamberreaches a predetermined pressure. The inorganic recording layer 12 isthen formed on the first protective layer 11 by sputtering the targetwhile introducing a process gas such as Ar gas or O₂ gas into the vacuumchamber.

(Film Forming Process of Second Protective Layer)

Next, the substrate 1 is transported into a vacuum chamber in which atarget for second protective layer film formation use is provided, andthe inside of the vacuum chamber is vacuumed until the vacuum chamberreaches a predetermined pressure. The second protective layer 13 is thenformed on the inorganic recording layer 12 by sputtering the targetwhile introducing a process gas such as Ar gas or O₂ gas into the vacuumchamber. As the sputtering method, it is possible to use ahigh-frequency (RF) sputtering method, a direct current (DC) sputteringmethod, or the like; however, the direct current sputtering method ispreferable. The reason is that since the direct current sputteringmethod has a high film forming rate compared to the radio frequencysputtering method, it is possible to improve productivity. Thus, theinformation signal layer L0 is formed on the substrate 1.

(Formation Process of Intermediate Layer)

Next, an ultraviolet curable resin is evenly coated over the informationsignal layer L0 by a spin coating method, for example. After thenpressing the concavo-convex pattern of a stamper on the ultravioletcurable resin that is evenly coated over the information signal layer L0and curing the resin by irradiating ultraviolet rays on the ultravioletcurable resin, the stamper is removed. In doing so, the concavo-convexpattern of the stamper is transferred on the ultraviolet curable resin,and for example, the intermediate layer S1 on which the in-grooves Ginand the on-grooves Gon are provided is formed over the informationsignal layer L0.

Here, the target for inorganic recording layer film formation, thetarget for the first protective layer formation, and the target forsecond protective layer formation will be described.

(Target for Inorganic Recording Layer Film Formation)

The target for the inorganic recording layer film formation may be a WCPmetal target with W, Cu, and Pd as main components, may be a WCPO oxidetarget with W oxide, Cu oxide, and Pd oxide as main components, and, inconsideration of productivity, the use of a metal target, which has maincomponents of W, Cu, and Pd for which DC sputtering capable of acomparatively rapid film formation rate is possible, is preferable. Theratio of W, Pd, and Cu included in the target preferably satisfies arelationship of 0.17≦x₁, more preferably 0.37≦x₁, still more preferably0.37≦x₁≦1.26, and most preferably 0.56≦x₁≦1.26. In addition, asdescribed above, x₁ is a variable defined by x₁=a/(b+0.8c).

The target for the inorganic recording layer film formation may be aWZPC metal target with W, Cu, Pd, and Zn as main components, may be aWZCPO oxide target with W oxide, Cu oxide, Pd oxide and Zn oxide as maincomponents, and, furthermore, may be a target mixing WZCPO of metal andoxide. In consideration of productivity, the use of a metal target,which has main components of W, Cu, Pd and Zn for which DC sputteringcapable of a comparatively rapid film formation rate is possible, ispreferable. The ratio of W, Pd, Cu and Zn included in the targetpreferably satisfies a relationship of 0.17≦x₂, more preferably 0.37≦x₂,still more preferably 0.37≦x₂≦1.26, and most preferably 0.56≦x₂≦1.26. Inaddition, as described above, the variable x₂ is a variable defined byx₂=(0.1d+a)/(b+0.8c).

As the WCP target for inorganic recording layer film formation, the WCPOtarget and the WZCP and WZCPO targets, ones having the same compositionas the inorganic recording layer 11 are preferable.

(Target for Forming First Protective Layer and Target for Forming SecondProtective Layer)

At least one of the target for forming the first protective layer andthe target for forming the second protective layer preferably includesSIZ or IGZO as a main component and it is more preferable that bothtargets include SIZ or IGZO. When one of the target for forming thefirst protective layer and the target for forming the second protectivelayer includes SIZ or IGZO as a main component, it is preferable thatthe target for forming the first protective layer include SIZ or IGZO asa main component. By including SIZ or IGZO as the main component in thefirst protective layer 12 provided on the lower side surface of theinorganic recording layer 11, it is possible to further increase thepower margin in comparison to a case in which SIZ or IGZO is included asthe main component in the first protective layer 12 provided on theupper side surface of the inorganic recording layer 11. Further, whenSIZ is used, if the amount of highly conductive In oxide is great, DCsputtering becomes possible and productivity becomes high; however,conversely, if the amount of In oxide is too great, the extinctioncoefficient of thin film becomes great and the transmittance of theinformation signal layer is lowered. Hence, the In oxide ratio is notparticularly limited; however, it is preferable that the ratio beadjusted according to the desired characteristics and productivity ofthe information signal layer. In addition, in the IGZO, since both Inoxide and ZnO oxide have conductivity, when the total amount of In oxideand ZnO oxide is great, DC sputtering is possible and productivity ishigh, which is thus preferable. However, when the amount of In oxide istoo large, for the same reasons mentioned above similarly to SIZ, sincethe transmittance of the information signal layer deteriorates, it ispreferable that the ratio be adjusted according to the desiredcharacteristics of the information signal layer.

(Formation Process of Information Signal Layer and Intermediate Layers)

Next, similarly to the formation process of the information signal layerL0 and the intermediate layer S1 described above, the information signallayer L1, the intermediate layer S2, the information signal layer L2,the intermediate layer S3, and the information signal layer L3 aresequentially laminated over the intermediate layer S1 in such an order.At this time, by adjusting the film formation conditions or the targetcomposition as appropriate, the thicknesses or the compositions of thefirst protective layer 12, the inorganic recording layer 11, and thesecond protective layer 13 that configure the information signal layersL1 to L3 may be adjusted as appropriate. Further, by adjusting theconditions of the spin coating method as appropriate, the thicknesses ofthe intermediate layers S2 to S3 may be adjusted as appropriate.

(Formation Process of Light Transmission Layer)

Next, after spin coating a light-sensitive resin such as an ultravioletcurable resin (UV resin) over the information signal layer L3 by a spincoating method, for example, light such as ultraviolet rays isirradiated on the light-sensitive resin so that the resin is cured. Inso doing, the light transmission layer 2 is formed over the informationsignal layer L3.

The desired optical information recording medium is obtained by theabove processes.

Examples

Below, the present disclosure will be described in detail using testexamples; however, the present disclosure is not limited solely to thetest examples.

In the following, the information signal layers of the multi-layeroptical information recording medium will be referred to as the L0layer, the L1 layer, the L2 layer . . . in order from the substrate sidetoward the laser irradiation plane side.

The test examples will be described in the following order.

1. Material of the First Protective Layer and the Second ProtectiveLayer 2. PdO Material Other Than WZCPO 3. Forming Position of SIZ Layer4. Composition of Inorganic Recording Layer 5. Transmittance Range ofTwo-Layer Optical Information Recording Medium 6. Transmittance Range ofFour-Layer Optical Information Recording Medium <1. Material of theFirst Protective Layer and the Second Protective Layer> Test Example 1-1

First, a polycarbonate substrate with a thickness of 1.1 mm was formedby injection molding. Here, a concavo-convex surface with grooves wasformed on the polycarbonate substrate. Next, the first protective layer(lower side), the inorganic recording layer, and the second protectivelayer (upper side) were sequentially laminated over the polycarbonatesubstrate, thereby forming an L0 layer.

The material, the thickness and the film formation method of each layerof the L0 layer were as follows.

First Protective Layer (Lower Side)

-   -   Material: ITO (SnO₂:In₂O₃=10:90 (% by mass))    -   Thickness: 10 nm    -   Film forming method: DC sputtering

Inorganic Recording Layer

-   -   Material: WZCPO (Cu:Zn:Pd:W=30.0:30.0:30.0:10.0 (atomic ratio        (atomic %)))    -   Thickness: 30 nm    -   Film formation method: DC sputtering (O₂ reactive sputtering)

Second Protective Layer (Upper Side)

-   -   Material: ITO (SnO₂:In₂O₃=10:90 (% by mass))    -   Thickness: 10 nm    -   Film formation method: DC sputtering method

Next, ultraviolet curable resin (manufactured by Sony Chemical &Information Device Corporation, product name: SK5500B) was uniformlycoated over the L0 layer by spin coating. After then pressing theconcavo-convex pattern of a stamper on the ultraviolet curable resinthat was evenly coated over the information signal layer L0 and curingthe resin by irradiating ultraviolet rays on the ultraviolet curableresin, the stamper was removed. In this manner, an intermediate layerhaving grooves and a thickness of 15.5 μm was formed.

Next, the first protective layer, the inorganic recording layer, and thesecond protective layer were sequentially stacked on the intermediatelayer, thereby forming the L2 layer. Furthermore, the formation of theL1 layer was omitted.

The material of each layer of layer L2, the thickness and the filmformation method were as follows.

First Protective Layer (Lower Side)

-   -   Material: SIZ (SiO₂:In₂O₃:ZrO₂=35:30:35 (mol %))    -   Thickness: 10 nm    -   Film forming method: RF sputtering method

Inorganic Recording Layer

-   -   Material: WZCPO (Cu:Zn:Pd:W=35.0:25.0:10.0:30.0 (atomic ratio        (atomic %)))    -   Film formation method: DC sputtering (O₂ reactive sputtering)    -   Thickness: 40 nm

Second Protective Layer (Upper Side)

-   -   Material: SIZ (SiO₂:In₂O₃:ZrO₂=35:30:35 (mol %))    -   Thickness: 25 nm    -   Film formation method: RF sputtering method

Next, an ultraviolet curable resin was evenly coated over the L2 layerby a spin coating method and cured by the irradiation of ultravioletrays, whereby a resin layer having the same hardness as the intermediatelayer and a thickness of 31.0 μm was formed.

Next, by evenly coating an ultraviolet curable resin (manufactured bySony Chemical & Information Device Corporation, product name: SK8300)over the L1 layer by a spin coating method and curing the resin byirradiating ultraviolet rays, a light transmissive layer with athickness of 53.5 μm was formed.

In this manner, a two-layer optical information recording medium havingan L0 layer and an L2 layer was obtained. In such a two-layer opticalinformation recording medium, by forming the resin layer between the L2layer and the light transmissive layer, the L2 layer state is set to thestate of the L2 layer of a four-layer optical information recordingmedium in a simulated manner.

Test Example 1-2

An optical information recording medium was obtained in the same manneras in Test Example 1-1 apart from the materials, thicknesses and filmformation methods of the first protective layer and the secondprotective layer of layer L2 as shown below.

First Protective Layer (Lower Side)

-   -   Material: SIZ (SiO₂:In₂O₃:ZrO₂=30:40:30 (mol %))    -   Thickness: 10 nm    -   Film forming method: DC sputtering method

Second Protective Layer (Upper Side)

-   -   Material: SIZ (SiO₂:In₂O₃:ZrO₂=30:40:30 (molar ratio))    -   Thickness: 25 nm    -   Film forming method: DC sputtering method

Test Example 1-3

An optical information recording medium was obtained in the same manneras in Test Example 1-1 apart from the materials, thicknesses and filmformation methods of the first protective layer and the secondprotective layer of layer L2 as shown below.

First Protective Layer (Lower Side)

-   -   Material: IGZO (In₂O₃:Ga₂O₃:ZnO=25:25:50 (mol %))    -   Thickness: 10 nm    -   Film forming method: DC sputtering method

Second Protective Layer (Upper Side)

-   -   Material: IGZO (In₂O₃:Ga₂O₃:ZnO=25:25:50 (mol %))    -   Thickness: 25 nm    -   Film forming method: DC sputtering method

Test Example 1-4

An optical information recording medium was obtained in the same manneras in Test Example 1-1 apart from the materials, thicknesses and filmformation methods of the first protective layer and the secondprotective layer of layer L2 as shown below.

First Protective Layer (Lower Side)

-   -   Material: ITO (SnO₂:In₂O₃=10:90 (% by mass))    -   Thickness: 10 nm    -   Film forming method: DC sputtering method

Second Protective Layer (Upper Side)

-   -   Material: ITO (SnO₂:In₂O₃=10:90 (% by mass))    -   Thickness: 25 nm    -   Film forming method: DC sputtering method

Test Example 1-5

An optical information recording medium was obtained in the same manneras in Test Example 1-1 apart from the materials, thicknesses and filmformation methods of the first protective layer and the secondprotective layer of layer L2 as shown below.

First Protective Layer (Lower Side)

-   -   Material: Si    -   Thickness: 10 nm    -   Film forming method: DC sputtering method (N₂ reactive        sputtering)

Second Protective Layer (Upper Side)

-   -   Material: Si    -   Thickness: 25 nm    -   Film forming method: DC sputtering method (N₂ reactive        sputtering)

(Initial State Power Margin)

The initial state of the power margin of the L2 layer of the opticalinformation recording media of Test Examples 1-1 to 1-5 obtained in theabove-described manner was calculated as below. Using a disc tester(manufactured by Pulstec Industrial Co., Ltd., product name: ODU-1000),1-7 modulation data with a density of 32 GB per layer was recorded andreproduced with a recording wavelength of 405 nm and a recording linearvelocity of 7.69 m/s, and the random symbol error rate (SER) wascalculated. Such an SER was calculated with respect to the recordingpower, a low side with recording power in excess of 4×10⁻³ was set asPwl, a high side was set as Pwh, and the optimal power between Pwl andPwh was set as Pwo. At this time, the power margin PM was calculatedfrom Formula 1 below. Here, an SER of 4×10⁻³ is the upper limit value ofthe SER at which error correction does not fail. If the upper limitvalue is exceeded, defects are generated in the reproduction data andthe signal quality particularly deteriorates.

PM=(Pwh−Pwl)/Pwo  (1)

The results thereof are shown in FIGS. 2A to 4B and Table 1.

Table 1 shows the evaluation results of the optical informationrecording media of Test Examples 1-1 to 1-5.

TABLE 1 Test Example Test Example Test Example Test Example Test Example1-1 1-2 1-3 1-4 1-5 First Protective SIZ/SIZ SIZ/SIZ IGZO/IGZO ITO/ITOSiN/SiN Layer/Second Protective Layer Power Margin >32 >31 >30 20 >24(SER) [%] Film Formation RF DC DC DC RF Method Refraction Rate 1.89 2.032.06 2.23 1.89 SIZ: SiO₂—In₂O₃—ZrO₂ IGZO: In₂O₃—Ga₂O₃—ZnO RF: a radiofrequency sputtering method DC: a direct current sputtering method

The following may be understood from Table 1.

By using SIZ or IGZO as the material of the first protective layer andthe second protective layer, the power margin may be set as 30% or more.Here, when the power margin is 30%, it is possible to sufficientlyabsorb the influence of the precision of the recording power of aconsumer drive, variation of in-plane sensitivity of the opticalinformation recording medium, temperature of the optical informationrecording medium, and a decrease in the actual recording poweraccompanying warping due to humidity, thereby enabling favorablerecording with a low error rate. When SIZ is used as the material of thefirst protective layer and the second protective layer, it is possibleto further widen the power margin in comparison to a case where IGZO isused.

By using SIZ or IGZO as the material of the first protective layer andthe second protective layer, it is possible to improve the transmittanceof the information signal layer. Accordingly, it is possible to increasethe light quantity of the laser beam reaching the L0 layer positionedfurthest to the back of the light irradiation plane.

By setting the content of In oxide with respect to SIZ to a range of 40mol % or more and reducing the electric resistance of the target, it ispossible to perform film formation by a DC sputtering method.Accordingly, it is possible to improve the film formation rate andimprove productivity.

According to the above, in order to improve the power margin andmaintain a high transmittance, it is preferable to use SIZ and IGZO asthe material of the first protective layer and the second protectivelayer adjacent to the inorganic recording layer and particularlypreferable to use IGZO.

Further, in order to increase productivity, it is preferable that thecontent ratio of In oxide with respect to SIZ be set to 40 mol % ormore; however, since the transmittance of the information signal layerdeteriorates due to the extinction coefficient of the SIZ thin layerbecoming large when such a content ratio is excessive, it is preferableto select the ratio of the In oxide and the like in accordance with thetransmittance and productivity desired for the information signal layer.

<2. PdO Material Other than WZCPO>

Test Example 2

First, a polycarbonate substrate with a thickness of 1.1 mm was formedby injection molding. Here, a concavo-convex surface with grooves wasformed on the polycarbonate substrate. Next, the first protective layer(lower side), the inorganic recording layer, and the second protectivelayer (upper side) were sequentially laminated over the polycarbonatesubstrate, thereby forming an L0 layer.

The material, the thickness and the film formation method of each layerof layer L0 were as follows.

First Protective Layer (Lower Side)

-   -   Material: ITO (SnO₂:In₂O₃=10:90 (% by mass))    -   Thickness: 8 nm    -   Film forming method: DC sputtering method

Inorganic Recording Layer

-   -   Material: In₂O₃—PdO (In:Pd=50:50 (atomic ratio (atomic %)))    -   Film forming method: DC sputtering (O₂ reactive sputtering)    -   Thickness: 40 nm

Second Protective Layer (Upper Side)

-   -   Material: ITO (SnO₂:In₂O₃=10:90 (% by mass))    -   Thickness: 10 nm    -   Film forming method: DC sputtering method

Next, ultraviolet curable resin (manufactured by Sony Chemical &Information Device Corporation, product name: SK5500B) was uniformlycoated over the L0 layer by spin coating. After then pressing theconcavo-convex pattern of a stamper on the ultraviolet curable resinthat was evenly coated over the information signal layer L0 and curingthe resin by irradiating ultraviolet rays on the ultraviolet curableresin, the stamper was removed. In this manner, an intermediate layerhaving grooves and a thickness of 15.5 μm was formed.

Then, by sequentially laminating the first protective layer (lowerside), the inorganic recording layer, and the second protective layer(upper side) on the intermediate layer, layer L1 was formed.

The material, the thickness and the film formation method of each layerof layer L1 were as follows.

First Protective Layer (Lower Side)

-   -   Material: ITO (SnO₂:In₂O₃=10:90 (% by mass))    -   Thickness: 10 nm    -   Film forming method: DC sputtering method

Inorganic Recording Layer

-   -   Material: In₂O₃—PdO (In:Pd=70:30 (atomic ratio (atomic %)))    -   Film forming method: DC sputtering (O₂ reactive sputtering)    -   Thickness: 40 nm

Second Protective Layer (Upper Side)

-   -   Material: ITO (SnO₂:In₂O₃=10:90 (% by mass))    -   Thickness: 10 nm    -   Film forming method: DC sputtering method

Next, ultraviolet curable resin (manufactured by Sony Chemical &Information Device Corporation, product name: SK5500B) was uniformlycoated over the L1 layer by spin coating. After then pressing theconcavo-convex pattern of a stamper on the ultraviolet curable resinthat was evenly coated over the information signal layer L1 and curingthe resin by irradiating ultraviolet rays on the ultraviolet curableresin, the stamper was removed. In this manner, an intermediate layerhaving grooves and a thickness of 19.5 μm was formed.

Then, by sequentially laminating the first protective layer (lowerside), the inorganic recording layer, and the second protective layer(upper side) on the intermediate layer, layer L2 was formed.

The material, the thickness and the film formation method of each layerof layer L2 were as follows.

First Protective Layer (Lower Side)

-   -   Material: ITO (SnO₂:In₂O₃=10:90 (% by mass))    -   Thickness: 10 nm    -   Film forming method: DC sputtering method

Inorganic Recording Layer

-   -   Material: In₂O₃—PdO (In:Pd=70:30 (atomic ratio (atomic %)))    -   Film forming method: DC sputtering (O₂ reactive sputtering)    -   Thickness: 40 nm

Second Protective Layer (Upper Side)

-   -   Material: SIZ (SiO₂:In₂O₃:ZrO₂=40:30:40 (mol %))    -   Thickness: 10 nm    -   Film forming method: RF sputtering method

Next, ultraviolet curable resin (manufactured by Sony Chemical &Information Device Corporation, product name: SK5500B) was uniformlycoated over the L2 layer by spin coating. After then pressing theconcavo-convex pattern of a stamper on the ultraviolet curable resinthat was evenly coated over the information signal layer L2 and curingthe resin by irradiating ultraviolet rays on the ultraviolet curableresin, the stamper was removed. In this manner, an intermediate layerhaving grooves and a thickness of 11.5 μm was formed.

Then, by sequentially laminating the first protective layer (lowerside), the inorganic recording layer, and the second protective layer(upper side) on the intermediate layer, the L3 layer was formed.

The material, the thickness and the film formation method of each layerof the L3 layer were as follows.

First Protective Layer (Lower Side)

-   -   Material: SIZ (SiO₂:In₂O₃:ZrO₂=40:30:40 (mol %))    -   Thickness: 10 nm    -   Film forming method: RF sputtering method

Inorganic Recording Layer

-   -   Material: In₂O₃—PdO (In:Zn:Sn:Pd=70:30 (atomic ratio (atomic        %)))    -   Film forming method: DC sputtering method (O₂ reactive        sputtering)    -   Thickness: 40 nm

Second Protective Layer (Upper Side)

-   -   Material: SIZ (SiO₂:In₂O₃:ZrO₂=40:30:40 (mol %))    -   Thickness: 10 nm    -   Film forming method: RF sputtering method

Next, by evenly coating an ultraviolet curable resin (manufactured bySony Chemical & Information Device Corporation, product name: SK8300)over the L3 layer by a spin coating method and curing the resin byirradiating ultraviolet rays, a light transmission layer with athickness of 53.5 μm was obtained. In this manner, a desired opticalinformation recording medium was obtained.

(Power Margin)

The initial state of the power margin of layers L1 to L3 of the opticalinformation recording medium of Test Example 2 obtained in theabove-described manner was calculated in the same manner as TestExamples 1-1 to 1-5. The results are shown in FIG. 5.

The following may be understood from FIG. 5.

Even in a case where PdO-based material other than WZCPO is used in theinorganic recording layer, by using a SIZ layer on the surface of theinorganic recording layer, it is possible to widen the power margin incomparison with a case in which an ITO layer is used. Here, by using ITOonly for the first protective layer (lower side) and SIZ on the secondprotective layer (upper side) for the L2 layer and using SIZ for boththe upper and lower protective layers in the L3 layer in contrast to theL1 layer which uses ITO for both the upper and lower protective layers,it may be understood that the power margin is widened in order of L1,L2, and L3. Thus, it may be understood that SIZ has an effect on thehigh recording power margin. However, the case in which the WZCPO layerand the SIZ layer are combined has a greater degree of improvement inthe power margin.

Here, only the case where an SIZ layer is used as a first protectivelayer and a second protective layer is shown; however, it is consideredthat the same effect may be obtained even in a case of using an IGZOlayer as the first protective layer and the second protective layer.

<3. Forming Position of SIZ Layer> Test Example 3-1

An optical information recording medium was obtained in the same manneras in Test Example 1-4.

Test Example 3-2

An optical information recording medium was obtained in the same manneras in Test Example 3-1 apart from the materials, thicknesses and filmformation methods of the first protective layer and the secondprotective layer of layer L2 as shown below.

First Protective Layer (Lower Side)

-   -   Material: SIZ (SiO₂:In₂O₃:ZrO₂=40:30:40 (mol %))    -   Thickness: 10 nm    -   Film forming method: RF sputtering method

Test Example 3-3

An optical information recording medium was obtained in the same manneras in Test Example 3-1 apart from the materials, thicknesses and filmformation methods of the first protective layer and the secondprotective layer of layer L2 as shown below.

Second Protective Layer (Upper Side)

-   -   Material: SIZ (SiO₂:In₂O₃:ZrO₂=40:30:40 (mol %))    -   Thickness: 25 nm    -   Film forming method: RF sputtering method

Test Example 3-4

An optical information recording medium was obtained in the same manneras in Test Example 1-1.

(Power Margin)

The initial state of the power margin of layer L2 of the opticalinformation recording media of Test Examples 3-1 to 3-4 obtained in theabove-described manner was calculated in the same manner as TestExamples 1-1 to 1-5. The results are shown in FIG. 6.

The following may be understood from FIG. 6.

In a case where SIZ is used as the material of one of the firstprotective layer and the second protective layer, it is possible toimprove the power margin in comparison to a case where ITO is used asthe material of both the first protective layer and the secondprotective layer.

When SIZ is used as the material of the first protective layer (lowerside), it is possible to improve the power margin in comparison to acase where SIZ is used as the material of the second protective layer(upper side).

When SIZ is used as the material of both the first protective layer andthe second protective layer, it is possible to improve the power marginin comparison to a case where SIZ is used as the material of one of thefirst protective layer and the second protective layer.

Thus, from the viewpoint of obtaining a favorable power margin, it ispreferable that SIZ be used as the material of one of the firstprotective layer and the second protective layer, in particular, as thematerial of the first protective layer (lower side) and more preferablethat SIZ be used as the material of both the first protective layer andthe second protective layer.

Here, only the case where an SIZ layer is used as the first protectivelayer and/or the second protective layer has been shown; however, it isconsidered that the same effect may be obtained even in a case of usingan IGZO layer as the first protective layer and the second protectivelayer.

<4. Composition of Inorganic Recording Layer> Test Examples 4-1 to 4-15

First, a polycarbonate substrate with a thickness of 1.1 mm was formedby injection molding. Here, a concavo-convex surface with grooves wasformed on the polycarbonate substrate. Next, the first protective layer,the inorganic recording layer, and the second protective layer weresequentially laminated over the polycarbonate substrate by thesputtering method. The specific configurations of each layer were asfollows.

First Protective Layer

-   -   Material: SIZ, thickness: 10 nm

Inorganic Recording Layer

-   -   Material: WZCPO, thickness: 40 nm

Second Protective Layer

-   -   Material: SIZ, thickness: 10 nm

However, the target compositions were manufactured for each of TestExamples 4-1 to 4-15 so that the atomic ratios c, d, b, and a of each ofCu, Zn, Pd and W in the WZCPO of the inorganic recording layer becamethe values shown in Table 2.

Next, by evenly coating an ultraviolet curable resin (manufactured bySony Chemical & Information Device Corporation, product name: SK8300)over the second protective layer by a spin coating method and curing theresin by irradiating ultraviolet rays, a light transmission layer with athickness of 100 μm was obtained.

In this manner, a desired optical information recording medium wasobtained.

(Transmittance Evaluation)

The transmittances of the optical information recording media of TestExamples 4-1 to 4-15 obtained as described above with respect to arecording wavelength of 405 nm were measured using a spectrophotometer(manufactured by JASCO Corporation, product name: V-530). The resultsare shown in Table 2.

Next, as a way of making the linear approximation, using the measuredtransmittances and the atomic ratios c, d, b, and a, each coefficientwas determined by multiplying a coefficient by each ratio so that thesquare of a determination coefficient R is the greatest with the sum ofeach ratio of the W oxide and the Zn oxide with relatively smallextinction coefficients as the numerator and the sum of each ratio ofthe Pd oxide and the Cu oxide with relatively large extinctioncoefficients as the denominator. The results are shown in FIG. 7A. InFIG. 7A, the horizontal axis indicates the variablex(=0.1d+a)/(b+0.8c)), and the vertical axis indicates the transmittance.As illustrated in FIG. 7A, the linear approximation is represented byy=25.642x+45.441. Here, y indicates the transmittance [%] and xindicates (0.1d+a)/(b+0.8c).

(Optimum Recording Power Evaluation)

Using a disc tester (manufactured by Pulstec Industrial Co., Ltd.,product name: ODU-1000), 1-7 modulation data with a density of 32 GB perlayer was recorded and reproduced with a recording wavelength of 405 nmand a recording linear velocity of 7.69 m/s to calculate the recordingpower at which the i-MLSE value is the smallest, and such a recordingpower was taken as the optimum recording power Pwo. The results areillustrated in FIG. 7B.

Table 2 illustrates the composition ratios and the transmittances of theinorganic recording layers of Test Examples 4-1 to 4-15. FIG. 8 is agraph that illustrates the composition ratios of the inorganic recordinglayers of Test Examples 4-1 to 4-13.

TABLE 2 Atomic ratio Atomic ratio Atomic ratio Atomic ratio c of Cu d ofZn b of Pd a of W x, (0.1d + a)/ Transmit- [Atomic %] [Atomic %] [Atomic%] [Atomic %] (b + 0.8c) tance [%] Test Example 4-1 41.3 17.7 14.3 26.70.601 60 Test Example 4-2 43.4 17 10.9 28.7 0.666 62.6 Test Example 4-338.8 19.8 9.6 31.8 0.831 66.9 Test Example 4-4 41.1 24.7 7.8 26.4 0.71064.1 Test Example 4-5 32.4 41 5.6 21 0.796 67.1 Test Example 4-6 36.332.4 9.1 22.2 0.667 64.1 Test Example 4-7 29.5 29.5 14.8 26.2 0.759 63Test Example 4-8 33 30.1 5.9 31 1.053 71.6 Test Example 4-9 32.4 41 5.621 0.796 64.87 Test Example 4-10 33 26.5 9.5 31 0.937 70.1 Test Example4-11 31.9 35.3 4.4 28.4 1.067 73.3 Test Example 4-12 28.5 25 32.2 14.20.304 73.3 Test Example 4-13 68.1 0 25.5 16.4 0.205 73.3 Test Example4-14 58.11 0 25.5 16.39 0.228 51.28 Test Example 4-15 28.48 25.09 32.214.24 0.305 53.25

The following may be understood from the linear approximationillustrated in FIG. 7A.

For the transmittance to be equal to or greater than 50%, it ispreferable that the variable x be equal to or greater than 0.17.

For the transmittance to be equal to or greater than 55%, it ispreferable that the variable x be equal to or greater than 0.37.

For the transmittance to be equal to or greater than 60%, it ispreferable that the variable x be equal to or greater than 0.56.

For the transmittance to be equal to or greater than 78%, it ispreferable that the variable x be equal to or less than 1.26.

Here, in a multi-layer optical information recording medium, it ispreferable that the transmittances of information signal layers equal toor higher than the L1 layer (L1 layer, L2 layer, L3 layer, . . . ) beequal to or greater than 55%. The reason why a transmittance equal to orgreater than 55% is preferable will be described later. Here, with atwo-layer disc using a recording film composition other than WZCPO(ZnS—SiO₂—Sb—Sn, TePdO, and the like), in order to increase thereflectance of the L0 layer, it is preferable that the transmittance ofthe L1 layer be equal to or greater than 50%.

The following may be understood from the linear approximationillustrated in FIG. 7B.

It is seen that for the optimum recording power Pwo to be equal to orless than 20 mW, it is preferable that the transmittance be equal to orless than 78%. Here, the optimum recording power Pwo: 20 mW is the upperlimit value of the optimum recording power Pwo of a consumer drivedevice. If the upper limit value is exceeded, the recording powerbecomes insufficient and the signal properties deteriorate.

<5. Transmittance Range of Two-Layer Optical Information RecordingMedium> Test Examples 5-1 to 5-12

First, a polycarbonate substrate with a thickness of 1.1 mm was formedby injection molding. Here, a concavo-convex surface with grooves wasformed on the polycarbonate substrate.

Next, the first protective layer, the inorganic recording layer, and thesecond protective layer were sequentially laminated over thepolycarbonate substrate by the sputtering method, whereby an L0 layerwas produced. Here, the L0 layer is for use as a two-layer opticalinformation recording medium.

The specific configurations of each layer were as follows.

First Protective Layer

-   -   Material: ITO, thickness: 10 nm

Inorganic Recording Layer

-   -   Material: WZCPO, thickness: 26 nm to 30 nm    -   Composition ratio: a=10, b=30, c=30, and d=30

Second Protective Layer

-   -   Material: TaN, thickness: 6 nm to 16 nm

However, the film formation conditions were manufactured for each ofTest Examples 5-1 to 5-12 so that the thicknesses of the inorganicrecording layer and the second protective layer became the values shownin Table 3.

Next, by evenly coating an ultraviolet curable resin (manufactured bySony Chemical & Information Device Corporation, product name: SK8300)over the second protective layer by a spin coating method and curing theresin by irradiating ultraviolet rays, a light transmission layer with athickness of 100 μm was formed.

In this manner, an optical information recording medium having only anL0 layer was obtained.

(i-MLSE Evaluation)

The i-MLSE of the optical information recording media of Test Examples5-1 to 5-12 obtained as described above was calculated as below. Using adisc tester (manufactured by Pulstec Industrial Co., Ltd., product name:ODU-1000), the i-MLSE value was calculated by recording and reproducing1-7 modulation data with a density of 32 GB per layer with NA=0.85, arecording wavelength of 405 nm, and a recording linear velocity of 7.69m/s.

(Reflectance Evaluation)

The reflectances of the optical information recording media of TestExamples 5-1 to 5-12 obtained as described above were measured using adisc tester (manufactured by Pulstec Industrial Co., Ltd., product name:ODU-1000), with NA=0.85 and a recording wavelength of 405 nm. Here, thereflectance of a single-layer optical information recording mediummanufactured using only the L0 layer of a two-layer optical informationrecording medium is referred to as the reflectance of the L0 layeralone.

Table 3 shows the measurement results of the i-MLSE and reflectances ofthe optical information recording media of the Test Examples 5-1 to5-12.

TABLE 3 Material Thickness Material Thickness of First of First Materialof Thickness of of Second of Second Protective Protective RecordingRecording Protective Protective Reflectance i-MLSE Layer Layer (nm)Layer film (nm) Layer Layer (nm) (%) (%) Test Example 5-1 ITO 10 WZCPO30 TaN 12 12.5 10.6 Test Example 5-2 10 28 12 13.4 10.6 Test Example 5-310 26 12 14.3 11.1 Test Example 5-4 10 30 10 12.6 10.3 Test Example 5-510 28 10 12.9 10.4 Test Example 5-6 10 26 10 14.1 11.0 Test Example 5-710 30 8 12.3 10.3 Test Example 5-8 10 28 8 12.8 10.2 Test Example 5-9 1026 8 13.1 10.8 Test Example 5-10 10 26 6 11.5 9.8 Test Example 5-11 1026 14 15.2 11.6 Test Example 5-12 10 26 16 16.2 12.2 WZCPO: the mixtureof W oxide, Pd oxide, Cu oxide, and Zn oxide

FIG. 9A is a graph that illustrates the relationship between the i-MLSEand the reflectances calculated as described above. It is seen from FIG.9A that for the i-MLSE value of the L0 layer to be equal to or less than11%, it is important for the reflectance of the L0 layer to be equal toor less than 14%. Here, the i-MLSE value 11% is the upper limit valuethat is said to be error correctable by a consumer drive device.Although the reflectance was able to be improved by causing one or acombination of the first protective layer, the inorganic recordinglayer, and the second protective layer to be thinner than the above filmthicknesses, the i-MLSE values would then deteriorate. It is presumedthat the i-MLSE values deteriorate since the formation of bubbles duringrecording becomes inappropriate as a result of changes in the heataccumulation or heat release of the inorganic recording layer.

Test Examples 5-13 to 5-24

With a reflectance of the L0 layer alone calculated as described aboveof 14% as the premise, the reflectance of the L0 layer with respect tothe transmittance of the L1 layer of a two-layer optical informationrecording medium was calculated by the calculation. The results areillustrated in Table 4 and FIG. 9B. Here, if the transmittance of L1 isT and the reflectance of the L0 layer is R, R is calculated by Formula 2below.

R=14%(reflectance of L0 layer alone)×T ²  (2)

Table 4 illustrates the reflectances of the L0 layers alone, thetransmittances of the L1 layers, and the reflectances of the L0 layersof the optical information recording media of Test Examples 5-13 to5-24.

TABLE 4 Reflectance Reflectance of L0 Layer Transmittance of L0 Layeralone (%) of L1 Layer (%) (%) Test Example 5-13 14 30 1.3 Test Example5-14 14 35 1.7 Test Example 5-15 14 40 2.2 Test Example 5-16 14 45 2.8Test Example 5-17 14 50 3.5 Test Example 5-18 14 55 4.2 Test Example5-19 14 60 5.0 Test Example 5-20 14 65 5.9 Test Example 5-21 14 70 6.9Test Example 5-22 14 75 7.9 Test Example 5-23 14 80 9.0 Test Example5-24 14 85 10.1

It may be understood from FIG. 9B that for the reflectance of the L1layer of a two-layer optical information recording medium to be equal toor greater than 4%, it is important for the transmittance of the L layerto be equal to or greater than 55%. Here, the reflectance 4% of the L1layer is the lower limit value that is demanded for an informationsignal to be reproduced using a consumer two-layer compatible drivedevice.

<6. Transmittance Range of a Four-Layer Optical Information RecordingMedium> Test Examples 6-1 to 6-9

The i-MLSE of the L0 layer was measured when the transmittance of the L1layer alone of a four-layer optical information recording medium wasmade to vary. The results are illustrated in Table 5 and FIG. 9C. Here,since the recording properties of L1 are not the subject of interest,adjustment of the transmittance of the L1 layer was performed by theadjustment of the thickness of the inorganic recording layer accordingto the below conditions.

Specific film configurations of the L1 layer were as below.

First Protective Layer

-   -   Material: ITO, thickness: 7 nm

Inorganic Recording Layer

-   -   Material: WZCPO, thickness: 2 nm to 130 nm    -   Composition ratio: a=25, b=10, c=40, d=25

Second Protective Layer

-   -   Material: ITO, thickness: 10 nm    -   Specific film configurations of the L0 layer were as below.

First Protective Layer

-   -   Material: ITO, thickness: 8 nm

Inorganic Recording Layer

-   -   Material: WZCPO, thickness: 30 nm    -   Composition ratio: a=10, b=30, c=30, d=30

Second Protective Layer

-   -   Material: TaN, thickness: 10 nm

Table 5 illustrates the transmittances of the L1 layer, and the i-MLSEvalues of the L0 layers of the optical information recording media ofTest Examples 6-1 to 6-9.

TABLE 5 Thickness of Inorganic i-MLSE of Recording Layers TransmittanceL0 Layer of L1 Layer (nm) of L1 Layer (%) (%) Test Example 6-1 130 3514.6 Test Example 6-2 100 40 13 Test Example 6-3 80 45 12 Test Example6-4 60 50 11.2 Test Example 6-5 50 55 10.8 Test Example 6-6 40 60 10.5Test Example 6-7 30 65 10.2 Test Example 6-8 15 70 10 Test Example 6-9 275 10

It may be understood from FIG. 9C that for the i-MLSE value of the L0layer to be equal to or less than 11%, it is important for thetransmittance of the L1 layer to be equal to or greater than 55%. Here,the i-MLSE value 11% is the upper limit value that is error correctableby a consumer drive device. The reason is that in a case when thetransmittance of the L1 layer is low, since the signal amount of the L0layer decreases, it is thought that sufficient S/N for reproduction isnot obtained. Therefore, the higher the transmittance of the L1 layer,the better the signal properties of the L0 layer.

In this manner, it is seen that with a multi-layer optical informationrecording medium with two layers or four layers, it is preferable thatthe transmittances of information signal layers equal to or higher thanthe L1 layer (L1 layer, L2 layer, L3 layer, . . . ) be equal to orgreater than 55%.

Although the embodiments of the present disclosure have been describedin detail above, the present disclosure is not limited to theembodiments described above, and various modifications based on thetechnical ideas of the embodiments of the present disclosure arepossible.

For example, the configurations, methods, processes, shapes, materials,and numerical values exemplified in the embodiments described above areonly examples, and different configurations, methods, processes, shapes,materials, and numerical values may be used as necessary.

Further, the configurations, methods, processes, shapes, materials, andnumerical values of the embodiments described above may be combined withone another within a range which does not depart from the gist of thepresent disclosure.

Furthermore, although a case when the information recording mediumincludes a four-layer information signal layer has been described as anexample in the embodiments described above, the number of layers of theinformation signal layer is not limited thereto, and it is possible forthe information signal layer to have an arbitrary number of two or morelayers.

In addition, although a case when the present disclosure is applied toan optical information recording medium with a configuration in whichtwo or more information signal layers and a light transmission layer arelaminated in such an order on a substrate and in which recording orreproduction of information signals is performed by irradiating laserbeam on the information signal layers from the light transmission layerside has been described as an example in the embodiments describedabove, the present disclosure is not limited to such an example. Forexample, the present disclosure is able to be applied to an opticalinformation recording medium with a configuration in which two or moreinformation signal layers and a protective layer are laminated in suchan order on a substrate and in which recording or reproduction ofinformation signals is performed by irradiating laser beam on the two ormore information signal layers from the substrate side or to an opticalinformation recording medium with a configuration in which two or moreinformation signal layers are provided between two substrates and inwhich recording or reproduction of information signals is performed byirradiating laser beam on the information signal layers from the side ofone of the substrates.

Further, although a case where each layer of the optical informationrecording medium was formed by a sputtering method has been described asan example in the embodiments described above, the film formation methodis not limited thereto, and other film formation methods may be used. Asother film formation methods, for example, CVD methods (Chemical VaporDeposition: technique in which a thin film is separated from vapor usinga chemical reaction) such as heat CVD, plasma CVD, or light CVD, PVDmethods (Physical Vapor Deposition: technique in which a thin film isformed by agglomerating a material that is physically vaporized in avacuum on a substrate) such as vacuum deposition, plasma-assisteddeposition, or ion plating may be used.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2011-022182 filed in theJapan Patent Office on Feb. 3, 2011, the entire contents of which arehereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The invention is claimed as follows:
 1. An optical information recordingmedium comprising: a substrate; two or more information signal layersprovided on the substrate; and a cover layer provided on the informationsignal layers, wherein at least one layer out of the two or moreinformation signal layers is provided with an inorganic recording layerincluding Pd oxide, a first protective layer provided on a first mainsurface of the inorganic recording layer, and a second protective layerprovided on a second main surface of the inorganic recording layer, andat least one of the first protective layer and the second protectivelayer includes a compound oxide of Si oxide, In oxide and Zr oxide as amain component.
 2. The optical information recording medium according toclaim 1, wherein any one surface of sides of the substrate and the coverlayer is a light irradiation plane irradiated with light in order torecord or reproduce information signals on the two or more informationsignal layers, and a layer which is opposite to the light irradiationplane out of the first protective layer and the second protective layerincludes the compound oxide.
 3. The optical information recording mediumaccording to claim 1, wherein both the first protective layer and thesecond protective layer include the compound oxide as a main component.4. The optical information recording medium according to claim 1,wherein the inorganic recording layer includes W oxide, Pd oxide and Cuoxide as main components.
 5. The optical information recording mediumaccording to claim 4, wherein the inorganic recording layer furtherincludes Zn oxide.
 6. The optical information recording medium accordingto claim 1, wherein any one surface of sides of the substrate and thecover layer is the light irradiation plane irradiated with light inorder to record or reproduce information signals on the two or moreinformation signal layers, and at least one layer out of informationsignal layers other than an information signal layer which is furthestto the back of the light irradiation plane is provided with theinorganic recording layer, the first protective layer, and the secondprotective layer, and at least one of the first protective layer and thesecond protective layer includes the compound oxide as a main component.7. The optical information recording medium according to claim 1,wherein any one surface of sides of the substrate and the cover layer isa light irradiation plane irradiated with light in order to record orreproduce information signals on the two or more information signallayers, an inorganic recording layer of an information signal layerclosest to the light irradiation plane out of the two or moreinformation signal layers is provided with the inorganic recordinglayer, the first protective layer, and the second protective layer, andat least one of the first protective layer and the second protectivelayer includes the compound oxide as a main component.
 8. An opticalinformation recording medium comprising: a substrate; two or moreinformation signal layers provided on the substrate; and a cover layerprovided on the information signal layers, wherein at least one layerout of the two or more information signal layers is provided with aninorganic recording layer including Pd oxide, a first protective layerprovided on a first main surface of the inorganic recording layer, and asecond protective layer provided on a second main surface of theinorganic recording layer, and at least one of the first protectivelayer and the second protective layer includes a compound oxide of Inoxide, Ga oxide and Zn oxide as a main component.